Minor improvements

[pkulev]

Closes issue(s): [ # ]

Description of the changes:

• What's new:

  • tune weapons parameters
  • add make targets for two level of pylint checking (with and without warnings)

• Fixes:

  • linting
  • use new CI distro
  • fix bug with assigning method instead of method call

• Refactoring:

  • remove unused variables
  • rename Playership -> PlayerShip

[codecov-io]

Codecov Report

Merging #67 into master will increase coverage by 0.5%. The diff coverage is 41.66%.

@@            Coverage Diff            @@
##           master      #67     +/-   ##
=========================================
+ Coverage   61.44%   61.95%   +0.5%     
=========================================
  Files          39       39             
  Lines        2114     2142     +28     
=========================================
+ Hits         1299     1327     +28     
  Misses        815      815

Impacted Files	Coverage Δ
xoinvader/application/__init__.py	100% <ø> (ø)	:arrow_up:
xoinvader/menu.py	0% <ø> (ø)	:arrow_up:
xoinvader/ingame.py	0% <0%> (ø)	:arrow_up:
xoinvader/gui.py	0% <0%> (ø)	:arrow_up:
xoinvader/ship.py	0% <0%> (ø)	:arrow_up:
xoinvader/weapon.py	44.87% <0%> (ø)	:arrow_up:
xoinvader/tests/test_collision.py	98.87% <100%> (ø)	:arrow_up:
xoinvader/utils.py	96.12% <100%> (+0.05%)	:arrow_up:
xoinvader/tests/test_utils.py	100% <100%> (ø)	:arrow_up:
xoinvader/tests/test_background.py	100% <100%> (ø)	:arrow_up:
... and 2 more

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